Which type of specimen is less likely to be affected by external contamination?

Venous specimens are less likely to be affected by external contamination due to their collection process. When blood is drawn from a vein, the phlebotomist uses a sterile technique, typically involving the use of an antiseptic to clean the skin and reduce the risk of introducing contaminants from the surrounding environment. Additionally, venous blood is collected directly into a vacuum-sealed collection tube, which minimizes exposure to external factors.

In contrast, plasma specimens, capillary specimens, and urine specimens can be more susceptible to contamination. Plasma specimens, although collected under sterile conditions, can still be subject to contamination if the tube is not handled properly post-collection. Capillary specimens, which are obtained by puncturing the skin, can easily pick up contaminants from the skin surface. Urine specimens can be contaminated by bacteria or substances present in the collection container or from improper collection techniques, such as not following a clean-catch method.

Thus, the venous specimen represents a collection method that inherently reduces the likelihood of contamination in comparison to these other types.